Synthesis Of Complex Structure Star Polymers Based On Hyperbranched Polyglycerol

Design and synthesis of copolymer with complex architecture are always pursued by polymer chemists in past decades.Thanks to the development of controlled polymerization,some linear and nonlinear(such as comb-like,star, dendritic,hyperbranched) copolymers are synthesized by means of the combination of the controlled radical polymerization with ionic polymerization,.These special architectural copolymers may form abundant morphologies in selective solvent or in bulk and have potential applications in chemistry,physics and biology.Up till now, the publications on three-dimensional graft polymer brushes are so limited because of the difficulty in synthesis.It may attribute to the limitation of single polymerization methodology and defects in molecular design.However,it is a very exciting work to prepare this kind of special copolymers with unique properties,thus it is an important to explore a novel synthesis strategy for these copolymers with complicated three-dimensional structures.In this thesis,the sythesis and characterization of blocked-arm star polymers and mixed-arm star polymers are performed by the combination of "Controlled/Living" Polymerization(ATRP and RAFT) and the coupling reaction("Click" Reaction and ATNRC) is also used in the preparation process.Our work provided a universal method for the synthesis of three-dimensional graft polymer brushes with complicated structure.The essential results obtained are shown as follows:1.The well-defined hyperbranched polyglycerol(HPG) was prepared by anionic polymerization of glycerol using 1,1,1-trihydroxymethyl propane and methanol potassium as initiation system.After esterified with 2-bromoisobutyryl bromide by different proportion,the macroinitiator HPG-g-Br with 2-bromoisobutyryl groups in its periphery initiated the ATRP of styrene(St) to obtain star polymer HPG-g-PS.The star polymers with HPG core and PS-b-PtBA or PS-b-PAA block copolymer side chains could be successfully synthesized by sequential ATRP.In the whole preparation,no homopolymers of PS and PtBA were detected,and so the purification procedure was very simple.By detachment of PS and PS-b-PAA side chains from the HPG core,the reliable molecular weight of star polymers could be obtained.2.The remaining hydroxyl groups of HPG-g-PS could be further reacted with chain transfer agent S-1-dodecyl-S'-(α,α'-dimethyl-α"-acetic acid) trithiocarbonate (DDAT) to obtain HPG-g-PS/DDAT,then the mixed-arm star polymers, HPG-g-PS/PtBA and HPG-g-PS/PAA were successfully synthesized by sequential RAFT.It was found that the arm length and arm number exert great effect on the structure of star polymers with mixed-arms.The initiation efficiency of the DDAT in the core of star molecules was evaluated by the linear polymers formed by the cleavage of the ester bond between the core and the mixed-arm in the presence of sodium hydroxide.It was found only if the arm number of PS was less than 66 and the molecular weight of PS was lower than 1,800 Da,then high initiation efficiency(93%) of DDAT could be reached.3.A heterofunctional initiatiation system composed of 4-hydoxyl-2,2,6, 6-tetramethyl piperidyl-1-oxyl(HTEMPO) and diphenylmethyl potassium(DPMK) were used to initiate the polymerization of ethylene oxide to produce TEMPO-PEO. The latter was reacted with HPG-g-PS in the presence of CuBr and PMDETA to produce blocked-arm star polymer HPG-g-(PS-b-PEO) by atom transfer nitroxide radical coupling(ATNRC) reaction.The efficiency of the coupling reaction could reach 92%even there were 210 PS chains on one HPG core.4.The poly(styryl)lithium was capped by ethoxyethyl glycidyl ether(EEGE) to form the functionalized PS-EEGE with an activeω-hydroxyl group and anω'-ethoxyethyl-protected hydroxyl group.The alkyne group and bromide atom were introduced onto PS end by a series of modification of the functional group.The obtained polymer was used as the macroinitiator and the diblock copolymer PS-b-PtBA with an alkyne group at the junction point was obtained by the ATRP of tert-butylacrylate(tBA).HPG-g-N₃ was produced by azidation of HPG-g-Br.Finally, the "Click" reaction was preceded between the azide group and alkyne group using CuBr and PMDETA as catalyst.Thus,the mixed-arm star polymers HPG-g-PS/PtBA with identical PS and PtBA side chains was obtained.